This invention relates to anodized aluminum surface layers for metal products, and more particularly relates to novel and improved metal products with outer anodized layers as well as a method of manufacturing same which are characterized by possessing high yield strength and hardness. For the purpose of illustration but not limitation, the present invention will be described in connection with athletic implements and, in particular, golf club heads. It will be apparent that the invention is readily conformable for use in the manufacture of other products which have requirements for related properties or characteristics. Numerous attempts have been made to optimize the performance of golf clubs and particularly golf club heads to increase or improve their ball-striking capability both with respect to distance and accuracy. With the advent of metal golf club heads there has been a constant search for a metal alloy structure that would optimize performance without unduly increasing the cost of fabrication while at the same time complying with USGA rules governing golf club design and construction.
In the construction of metal clubs, especially the so-called metal woods, the basic materials used are forged carbon steels, investment or sand cast stainless steels, copper based, nickel based, or titanium based alloys. U.S. Pat. No. 5,037,102 to Fukayama describes a golf club head having a contact surface harder than the head and made up of a combination of aluminum or aluminum alloy combined with powdered ceramics. U.S. Pat. No. 4,768,787 to Shira utilizes alumina, or hardened aluminum, in forming a frictional contact surface, the hardened materials or particles protruding above the surface to provide greater frictional contact with the golf ball.
In U.S. Pat. No. 5,342,812 to Niskanen, et al a composite head utilizes in part an alumina material. U.S. Pat. No. 5,458,334 to Sheldon, et al discloses a process for making golf club heads by electro-spark deposition. U.S. Pat. No. 2,908,502 to Bradstreet, et al discloses a golf club head having an impact surface coated with a roughened, granular crystalline oxide coating which is selected from the group consisting of routile and alumina. Other representative patents are those U.S. Pat. No. 5,207,427 to Saeki; U.S. Pat. No. 5,472,202 to Yamanaka; U.S. Pat. No. 5,486,223 to Carden; U.S. Pat. No. 5,487,543 to Funk; and U.S. Pat. No. 5,531,444 to Buettner.
Notwithstanding the ever-increasing activity in this field and attempts to improve club head design and construction, no one to the best of my knowledge has successfully devised a lightweight aluminum golf club head with a hard anodized alumina surface. xe2x80x9cHard anodizingxe2x80x9d is the process which produces a substantially heavier coating or surface layer than conventional anodizing for a given length of time. Alumina crystallizes in a hexagonal system, is very stiff and has a density of 3.99 g/cm3 which will not materially affect the total weight of the club head. The aluminum density being on the order of 2.7 g/cm3, the overall size of the club head can be larger than existing metal club heads, and the total weight of the head can still be within the maximum 205 g allowed by USGA rules. It has been found that the enlarged head size and striking surface greatly minimizes distortion or twisting when contacting the golf ball thereby reducing any tendency to slice or hook the ball. Other advantages include minimal costs of fabrication, ability to undergo violent shock without cracking, improved life and ball-striking characteristics owing to the strong adherence of the anodized layer(s) to the aluminum body of the head as well as uniformity of thickness of the layer(s).
The characteristics of the hard-anodized layer can be greatly enhanced by utilizing in combination with an inner core or layer of high hardness in excess of 90 Brinell or xe2x80x9cHBNxe2x80x9d. Optimally, the inner layer is a metal or metal alloy which is precipitation hardened followed by reverse quenching to result in a hardness on the order of 190-210 HBN or higher. The reverse quenching, in which the article is successively exposed to a low temperature liquid followed by a higher temperature liquid, has been found to dramatically reduce cracking in the outside anodized layer of the resultant product.
It is therefore an object of the present invention to provide for novel and improved method of manufacturing athletic implements, particularly those of the type having a ball-striking surface.
It is another object of the present invention to provide for a novel and improved large anodized aluminum golf club head and method of manufacturing same characterized by possessing a high yield strength, hardness, coefficient of restitution and wear resistance of the anodized surface layer or layers together with a high damping capacity, toughness and low density of the resultant head.
It is a further object of the invention to provide for a novel and improved metal product having a hard inner layer or sublayer and at least one anodized surface layer covering or partially covering the inner layer to achieve a material having an average hardness on the order of about 300 to 350 HBN.
It is an additional object to provide for a novel and improved method of manufacturing an aluminum alloy product having a hard anodized outer layer and wherein the inner or sublayer is composed of an aluminum alloy subjected to precipitation hardening and reverse quenching prior to combining with the outer layer; and further wherein the resultant article is characterized by being lightweight, high hardness and minimal cracking in the outer anodized layer.
In accordance with the present invention, there has been devised a novel and improved product or structure having a sublayer of a first aluminum alloy material and a hard anodized alumina outer surface layer at least partially covering said first material. Preferably, the product is a golf club head wherein the sublayer or body is hollow and composed of an aluminum alloy, and the outer surface layer is hard-anodized onto at least a portion of an external surface of the body to form a layer of alumina of predetermined thickness. It has been discovered that the hardness of the sublayer strongly influences that of the outer layer, and that the method of manufacture of the inner layer can substantially reduce the cracking of the hard-anodized outer layer thereby enabling the outer layer to be formed of increased thickness and further increase the hardness and related properties of the final product. The resultant product lends itself well to use in the manufacture of other products, such as, pump casings and other pump parts in that their wear resistance is related to hardness, for example, in combating abrasion from foreign particles passing through the pump.
The above and other objects, advantages and features of the present invention will become more readily appreciated and understood from a consideration of the following detailed description of preferred and modified forms of the present invention when taken together with the accompanying drawings in which: